Abstract

Characteristics of the algal flora and the water chemical parameters of some tropical lakes in the valley of the Rio Doce (Brazil, Minas Gerais State) were investigated. The collected samples included 9 species of the Dinophyta division. Besides the well known pantropical/temperate taxa two others, Peridinium baliense (considered earlier as narrowly endemic in the Indo-malayan region) and a previously undescribed species was found. These two latter taxa proved to be subdominant in the plankton samples. Both taxa are described and illustrated by drawings and light micrographs. The new species shares features with P. baliense, which belongs to the lomnickii section, but has completely different hypothecal plate structure and shows differences in its ecology as well. These differences allow us to conclude that this taxon is a new species, consequently the name P. brasiliense sp. nova is proposed. Although in the taxonomy of freshwater dinoflagellates the hypothecal plate arrangement is usually neglected, our results indicate that taxonomic weight of this feature sometimes might be remarkable. Quantitative analysis of the microvegetation suggests that the large sized dinoflagellates, owing to their capability of active locomotion can be important members of the phytoplankton in stratified tropical lakes.
Selected physical and chemical environmental data are presented for the investigated localities.